The use of transition metal chelates as catalysts for bleaching agents is well known in the art. For example, U.S. Pat. No. 4,119,557, issued to Postlethwaite, discloses the use of iron-polycarboxyamine complexes with hydrogen peroxide releasing substances to clean fabrics. Similarly, U.S. Pat No. 5,244,594 (Favre et al.), U.S. Pat. No. 5,246,621 (Favre et al.), U.S. Pat. No. 5,194,416 (Jureller et al.), and U.S. Pat. No. 5,314,635 (Hage et al.) describe the use of manganese complexes of nitrogen--(or other heteroatom--) coordinated macrocycles as catalysts for peroxy compounds.
The utility of compounds of this type has motivated researchers to develop new ligands that both stabilize the catalyst complex and that are able to withstand an oxidative environment. Promising ligands in this respect are the tetraamido macrocycles represented by structure 10 shown in FIG. 1 which, when complexed with a transition metal such as iron, afford particularly good dye transfer inhibition capabilities.
An azide-based synthesis of the macrocycle is described by Collins et al. in J. Am. Chem. Soc., vol. 113, No. 22, page 8419 (1991). A problem with this synthesis is that it produces the tetraamido macrocycle in yields of only about 12% (starting from 1,2-phenylenediamine, as shown in the scheme at page 8422 of the article) and employs isolation techniques which cannot be adapted to large scale production. (Note: The identical synthesis is described by Erich S. Uffelman in his Ph.D. dissertation at California Institute of Technology (1992) and is the work upon which the synthesis of the journal article is based.)
Another synthetic route to the rnacrocycle is described in U.S. Pat. No. 5,853,428, issued also to the same Collins, and employs a ring forming strategy that is the reverse of the earlier published synthesis. In this synthesis, .alpha.-aminoisobutryic acid is used as a starting material to form the intermediate diacid 18 shown in FIG. 1, which is then coupled with an aryl diamine to yield the macrocycle (as shown in the scheme at col. 15 of the patent). This later synthesis, described by Collins as now being his preferred synthesis, provides the macrocycle structure in two steps and in an improved overall yield of about 18% (starting from diethyl malonyl dichloride). (Note: The identical synthesis is described by Scott W. Gordon-Wylie in his Ph.D. dissertation at Carnegie Mellon University (1995) and is the work upon which the synthesis of the patent is based.)
However, a number of problems exist with the Collins patent synthesis. For one, .alpha.-aminoisobutyric acid is a relatively expensive starting material. Further, the yield of the diacid is only about 50-60% from that starting material and usually requires ether purification. Additionally, the first step, a double coupling, is said to require 72-144 hours for completion, while the second step, a ring closure, requires 48-110 hours. Still further, the use of large amounts of anhydrous pyridine as solvent are apparently required in both steps, which is commercially prohibitive. For commercial purposes, a more efficient and less expensive synthesis of the tetraamido macrocycle is required than is provided by either of the two prior art syntheses just described.